fix casting to ISC_SHORT/ISC_LONG

without this, ib_fill_isqlda sends zeroes on
big-endian 64-bit architectures.
https://buildd.debian.org/status/fetch.php?pkg=libdbd-firebird-perl&arch=s390x&ver=1.14-1&stamp=1378735413
http://buildd.debian-ports.org/status/fetch.php?pkg=libdbd-firebird-perl&arch=ppc64&ver=1.12-1&stamp=1377471653
http://buildd.debian-ports.org/status/fetch.php?pkg=libdbd-firebird-perl&arch=sparc64&ver=1.12-1&stamp=1376623406
release 1.15